Recovery of electroplate utilizing molten lead



United States Patent 01 fice 3,442,643 Patented May 6, 1969 3,442,643 RECOVERY OF ELECTROPLATE UTILIZING MOLTEN LEAD Ernest B. Ackerman, 1537 N. Marion, Denver, Colo. 80218 No Drawing. Filed Dec. 8, 1965, Ser. No. 512,519

Int. Cl. C22b 11/04 US. CI. 75-63 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to a novel method for reclaiming metals which have been electrodeposited on base metals and/or non-metallic materials. More particularly, the invention is directed to a simple and economical method for reclaiming precious metals such as the noble metals and those metals of a less precious nature from a base material such as brass, bronze, copper, aluminum, steel, iron, and the like.

In the present economy where precious metals such as gold, silver, and particularly platinum and palladium are becoming more scarce as a result of increased industrial use, the salvaging of the aforesaid materials which have been electrodeposited upon base metals, or from materials where the precious metals are used in admixture with a base metal, is becoming increasingly important.

Although various methods have been used in the past, and are in present use, for the recovery of precious metals, such methods are accompanied by serious disadvantages. For example, methods for recovering electroplate by oxidation, such as dissolution of the metal plate in solvents such as an acid or cyanide solution, are undesirable because of the toxic nature of the chemicals employed and in view of the need for replenishing the chemicals consumed in the process. Electrolytic oxidation, on the other hand, is relatively expensive and, further, the process is not completely controllable.

Accordingly, it is an object of the present invention to provide a simple and economical method for the recovcry of precious metals associated with base metals.

A further object is to provide a method of recovering precious metals from base metals wherein the need for expensive complex equipment is eliminated and wherein metal solvents are employed which can be continuously re-used without replacement.

The aforesaid and other objects will be apparent from the following detailed description with particular em phasis being placed on the working example.

According to the present invention, an article from which the precious metal is to be removed is contacted with a metal solvent in a bath maintained at a temperature above the melting point of the precious metal to be recovered, and possibly above the melting point of the base metal associated with the precious metal. The precious metal is melted in the bath and brought into solution with the metal solvent of the bath. Thereafter, the precious metal is removed from the metal bath, preferably by adding minor amounts of a second metal which is incompatible with the solvent metal of the bath, and is a better solvent for the precious metal to be recovered than the metal solvent of the bath. Upon stirring of the bath, the precious metal is taken up by the second metal, with the combined metals forming a distinct layer on top of the bath. The layer is removed and the precious metal recovered by known techniques.

More particularly, in accordance with the invention, a metal such as lead is placed in a container and heated to its molten state and above the melting point of the precious metal and possibly the base metal from which the precious metal is to be separated. The material from which the precious metal is to be salvaged is contacted with the molten lead until the precious metal is completely melted and flows into the molten lead. Possibly, the base metal will also be dissolved by the aforesaid operation. Thereafter, minor amounts of zinc are added to the bath. Since the zinc does not mix with the molten lead and is a better solvent for the precious metal than the lead of the bath, the lead will release the precious metal to the zinc. The zinc with the precious metal dissolved therein will rise to the top of the molten lead bath for removal. The precious metal is separated from the zinc and any traces of lead by cupellation, electrolytic techniques, distillation or precipitation methods, or the like.

The precious metals which are salvaged by the method of the present invention include the noble metals such as gold, silver, platinum, rhodium, palladium, iridium, ruthenium, osmium, and other less noble metals such as cadmium, nickel, and copper. The metal solvent making up the bath will vary depending upon the precious metal to be recovered. It is only essential that the metal solvent bath have the ability to dissolve the precious metal when in the liquid state. The preferred metal for use herein in view of its availability and other desirable characteristics is lead. However, other metals including zinc, mercury, antimony, and cadmium can be employed. In the event a second metal is used in the process for recovering the precious metal, it must be judiciously selected and possess the properties of being incompatible with the metal solvent, and a better solvent for tlre precious metal than the solvent metal of the bath. For this reason, when lead is employed as the solvent metal, zinc is the preferred second metal. Again, however, depending upon the precious metal to be recovered, other metals can be selected. Moreover, it is possible, although not preferred, to recover the precious metal from the molten bath directly by distillation or precipitation methods, avoiding the use of the second metal. However, inasmuch as the base metal may be melted in the process, complications in the aforesaid methods may exist. The temperature of the opera-tion again is not critical, with it only being necessary that the molten bath be above the melting point of the precious metal in order that the precious metal exists in the molten bath in the liquid state. Normally, the operating temperature of the bath will be only slightly above the melting point of the precious metal. The base metal is removed from the molten solvent bath as a precipitate from the bottom of the kettle, in the event the base metal is melted. In the event the base metal has a higher melting point than the temperature of the bath, the articles from which the precious metal is to be salvaged can merely be dipped into the molten solvent bath in a mesh basket or the like and removed after the precious metal has melted. The most desirable procedure to be employed will be apparent to one skilled in the art having this specification as a guide.

The invention will be more fully understood by reference to the following working embodiment. It is to be 3 appreciated, however, that this embodiment is included herein only for illustrative purposes and is not to be construed as a limitation to the scope of the invention.

EXAMPIJE Five-hundred pounds of pure lead was placed in a kettle and brought to an operating temperature of about 1500 C. A basket of materials which contained a layer of silver electrodeposited thereon was lowered into the molten bath by means of an overhead conveyor. The basket and the parts remained in the bath for approximately ten minutes at which time the basket of materials was raised from the bath. The silver layer electroplated onto the materials was completely removed and remained in the molten bath.

Approximately two percent of zinc based on the weight of the lead was added to the saturated lead bath which combined with the dissolved silver to form intermetallic compounds or materials. The temperature of the bath was then slowly lowered during which time t he alloys having a lower density and higher melting point floated to the surface of the bath and formed a distinct layer. The layer was skimmed off and the silver recovered by known cupellation methods.

As will be apparent, in the aforesaid example, the lead in the bath can be replaced by other materials including zinc, mercury, bismuth, antimony, and alloys thereof. Additionally, the second metal which is used to selectively absorb the precious metal can be replaced by other materials. As noted hereinbefore, the selection of the solvent bath and the second metal for the selective absorption of the precious metal will depend upon the material being salvaged. It is obvious from the above description that the invention is not limited to the embodiments set forth herein. Modifications can be made by one skilled in the art without departing from the scope of the invention disclosed. Such modifications and departures are to be covered herein with the invention only being limited in accordance with the appended claims.

It is claimed;

1. The process of recovering precious metals selected from the group consisting of gold, silver, platinum, rhodium, palladium, osmium, iridium, and ruthenium electroplated onto a base metal comprising (1) contacting the article from which the precious metal is to be salvaged with lead maintained at a temperature above the melting point of the precious metal, said precious metal being melted and dissolved by the lead; (2) adding zinc to the lead and precious metal admixture; (3) stirring said admixture to contact said precious metal with said zinc; (4) removing said zinc having said precious metal dissolved therein from the lead; and (5) recovering said precious metals from the zinc.

References Cited UNITED STATES PATENTS 147,454 2/1874 Webster et al. -83 X 312,847 2/1885 Harris 75-83 539,795 5/1895 Christmas 75-83 X 718,089 1/1903 Carpenter 75-83 735,032 7/1903 Carpenter 75-83 1,160,590 11/1915 Foersterling et a1. 75-63 X 1,428,041 9/1922 Kroll 75-63 X 1,562,472 11/1925 Pederson 75-63 2,683,085 7/ 1954 Lohberg 75-63 3310, 182 10/1965 Funari 75-63 L. DE-WAYNE RUTLEDGE, Primary Examiner. HENRY W. TARRING II, Assistant Examiner.

US. Cl. XJR. 75 s3; 209- 

